SW3220306_Response To Comments_20221020

LandDes*n
CREATING PLACES
THAT MATTER.
October 20, 2022
Jim Farkas
Environmental Engineer
North Carolina Department of Environmental Quality
Division of Energy, Mineral, & Land Resources — Stormwater Program
512 N. Salisbury Street
1612 Mail Service Center
Raleigh, NC 27699-1612
RE: Preserve at Forest Creek LID PN 1020233
Stormwater Permit No. SW3220306
Dear Mr. Jim Farkas,
1. Prior Comment 1.a.ii — "Offsite portions of the drainage area to an SCM must be accounted for at their
full build -out potential (15A NCAC 02H .1003(3)(b))" Updated SCM sizing calculations do not appear to have
been provided (taking into account the more impervious drainage areas. Please provide the updated SCM
sizing calculations based on the most recent SCM drainage area information.
LDI Response: Wet Pond sizing has been revised per updated drainage area information.
2. Prior Comment 1.a.iii.1 — "Supplement-EZ Form, Wet Pond Page, Line 2..." As indicated above, the
minimum required treatment volumes do not appear to be recalculated based on the most recent drainage
area information. For example, Wet Pond 1 shows a minimum required treatment volume of 18,580 cf (taken
from the March 16, 2022 submission calculations) but calculating the minimum required treatment volume
for this SCM based on the most recent DA information (Drainage Area = 491,598 sf, Impervious Area =
302,101 sf) results in a minimum design volume of approximately 24,700 cf (%BUA = 61.5%, Rv = 0.603,
Volume = 24,700 cf), this issue is also present with the other SCMs. Please revise as needed. NOTE:
Revised sizing calculations were provided for Wet Pond 6 in the revised calculation booklet (Revised June
2022), however, they indicate that the drainage area to this SCM is 8.31 ac (=361,980 sf) and that the
impervious are within this drainage area is 2.49 ac (=108,460 sf). These calculations were not reviewed
since they do not appear to be related to the drainage area information for Wet Pond 6 as shown in the
other submittal documents (Drainage Area = 291,243 sf & Impervious Area = 259,543 sf).
LDI Response: Minimum required treatment volume has been updated for each SCM using the DA
information provided on the DA worksheet. Wetpond 6 DA information has been updated to reflect the
revised DA (361,823 sf DA with 259,543 sf of impervious).
3. Prior Comment 1.a.iii.3 — "Supplement-EZ Form, Wet Pond Page, Line 26..." The main concern with
the original comment appears to be addressed, however, there still appears to be issues with the
information shown for Wet Ponds 2, 3, 5, & 6. For example, the form shows the surface area of the main
pool at the permanent pool elevation for Wet Pond 2 as 6,076 sf while the provided stage -storage tables
indicate 6,266 sf. This issue is also present with the other noted SCMs. Please revise as needed.
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LDI Response: Surface area of the main permanent pool and volume of the main permanent pool have been
updated for Wet Ponds 1, 2, 3, 5, & 6.
4. Prior Comment 1.a.iii.4 — "Supplement-EZ Form, Wet Pond Page, Line 27..." Similar to the prior
comment, the original comment appears to be addressed, but there still appear to be issues with the values
shown for Wet Ponds 2, 3, 5, & 6. For example, the form shows the permanent volume of the main pool for
Wet Pond 2 as 19,756 cf while the provided stage- storage tables indicate 20,418 cf. This issue is also
present with the other noted SCMs. Please revise as needed.
LDI Response: Surface area of the main permanent pool and volume of the main permanent pool have been
updated for Wet Ponds 1, 2, 3, 5, & 6.
5. Prior Comment 2 — "It appears as though some of the plans... are not signed (Section V1,8 and 15A
NCAC 02H .1042(2)(g)). Please provide signed copies of the applicable plans." Please provide 2x hard
copies and 1x electronic copy of signed plan sheets C104, C 200, C208, C500-506, & C708-713. These
items were not provided with the prior submission.
LDI Response: All revised sheets to be signed and submitted.
6. Prior Comment 4 — "Please ensure that the SCM maintenance access and easements are sufficiently
large to allow for access and maintenance to the entire SCM (General MDCs 8 & 9)..." The SCM
maintenance access and easements do not appear to include the entire SCM systems, most of the outlet
structures and emergency spillways are not included within the easement. Please revise as needed. The
entire footprint of the SCM system must be included in the access and maintenance easement, plus an
additional 10 ft or more (25 ft is recommended for wet ponds due to the nature of their maintenance
requirements) around the SCM to provide enough room to complete maintenance tasks. This SCM system
includes the side slopes, forebay, riser structure, SCM device, and basin outlet, dam embankment, outlet,
and emergency spillway.
LDI Response: SCM maintenance access easements have been extended to include all outlets and
emergency spillways.
7. Prior Comment 7.d.i — "Please correct the following issues with the Application, Section IV, 10 —
Please ensure that the off -site portions of the drainage areas are accounted for." The off -site drainage area
information for Wet Pond 6 does not appear to be correct, the off- site drainage area is shown as 58,500 sf
and the off -site BUA is shown as 95,929 sf. Please revise as needed.
LDI Response: Offsite DA has been revised. Offsite DAs are assumed to have full build out.
8. Prior Comment 8.b.i.1 — "Please correct the following issues with the Supplement-EZ Form, Drainage
Area Page, Lines 7, 5, & 11..." As noted above, please revise the off -site drainage area information for Wet
Pond 6 as needed. Please also remove the off -site components from the Entire Site Column (The entire Site
Column is not a summation of the values shown in the other columns, but rather an accounting of the entire
site).
LDI Response: Wet Pond 6 DA information has been revised. Offsite DA information REMOVED FROM
Entire Site column.
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9. Prior Comment 8.b.ii.1 — "Please correct the following issues with the Supplement-EZ Form, Drainage
Area Page, Entire Site Column..." As noted above, the Entire Site Column is an accounting of the entire
project area (similar to how the drainage area columns are an accounting of the drainage areas), not just a
sum of the drainage area columns. All BUA located on -site (whether it drains to an SCM or not) should be
included in this column. There are typically no off -site components to the Entire Site Column (since off -site
areas are not part of the entire site). Please refer to the other comments to address issues with Lines 5-8,
11, & 18 of this column.
LDI Response: Offsite DA information has been removed from Entire Site column.
10. Prior Comment 8.b.ii.2 — "Please correct the following issues with the Supplement-EZ Form, Drainage
Area Page, Entire Site Column, Lines 5-7..."
a. Line 5 — The "total drainage area" of the entire site is equal to the project area. The value shown here
(4,836,757 sf = 111.04 ac) does not correspond to the project area as shown in Section IV, 7 of the
Application (101.65 ac). Please revise as needed.
LID Response: Total Drainage Area revised to reflect Total Project Area.
b. Line 6 — The "on -site drainage area" of the entire site is equal to the project area. The value shown
here (4,569,900 sf = 104.91 ac) does not correspond to the project area as shown in Section IV, 7 of the
Application (101.65 ac). Please revise as needed.
LID Response: On -Site Drainage Area has been revised to reflect Total Project Area.
C. Line 7 — The "off -site drainage area" of the entire site is equal to zero since there are no areas that are
both part of the entire site and not located on -site. Please revise as needed.
LDI Response: Off -Site Drainage Area has been revised.
11. Prior Comment 8.b.ii.3 — "Please correct the following issues with the Supplement-EZ Form, Drainage
Area Page, Entire Site Column, Line 18..." This item (44%) should correspond to Section IV, 8 of the
Application (47.8%). Revise either as needed. Information about calculating project density can be found in
15A NCAC 02H .1003(1).
LID Response: Entire Site Column, Line 18 has been revised per updated DA and BUA. Section IV, 8 has
been revised based on updated Line 18 item.
12. Prior Comment 9.a — "Provide PDFs of all revisions..." Electronic files from the June 24, 2022
submission were not uploaded through the online portal. Please provide these files in addition to the files
needed to address these comments.
LID Response: Electronic files for 3rd submittal to be submitted through online portal.
13. Wet Pond 3 —As designed, Wet Pond 3 does not appear to have a sufficiently large main pool surface
area (Wet Pond MDC 1). Per the provided drainage area information,
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the %BUA for the drainage area is 67.3% and the average depth of the main pool is calculated as 3.2 ft.
This results in an SA/DA table value of approximately 2.32% (interpolated) which results in a minimum
required main pool surface area of approximately 25,940 sf while only 19,510 sf of surface area is provided.
Please revise
LID Response: Wet Pond 3 has been revised to provide 27510 sf of surface area.
14. Wet Pond 4 — The lowest bypass weir for this pond is located at elevation 586.35'. Interpolating the
storage volume that is provided by the temporary pool at this surface water elevation results in 29,236 cf of
storage. The minimum required storage volume for this Wet Pond is approximately 33,700 cf. Please ensure
that at least the minimum design volume for this pond can be stored between the permanent pool and the
lowest bypass weir (General MDC 1).
LID Response: Bypass weir has been relocated to 586.55' to achieve the minimum required storage volume.
15. Please correct the following issues with the Application:
a. Section IV, 10, Drainage Area 4 — The % Impervious Area value (46.4%) does not appear to be
correct. Please revise as needed.
LID Response: % Impervious Area values revised for all drainage areas per revised drainage area
information.
b. Section IV, 10, Drainage Area 6 —As mentioned above, please revise the off -site drainage area
information as needed.
LID Response: Off -Site Drainage Area information revised for all drainage areas per revised drainage area
information.
C. Section VIII — Since Mason Greeson is no longer associated with the project, please update this
information.
LID Response: David Gusty will now be the consulting engineer.
16. Please correct the following issues with the Supplement-EZ Form:
a. Cover Page:
i. Line 2 — The project area information (105.5 ac) should correspond to the project area as shown in
Section IV, 7 of the Application (101.65 ac). Please revise as needed.
ii. Lines 27-32 — Please update this information as needed.
LID Response: Cover Page project information has been revised. David Gusty will now be the certifying
designer
b. Drainage Area Page:
i. Drainage Area 6, Lines 7 & 11 — Revise as needed in accordance with other comments.
ii. Entire Site Column, Lines 5-8, 11, & 18 — Revise as needed in accordance with other comments.
iii. Line 20 — Revise as needed in accordance with other comments.
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LID Response: Drainage area 6 Off -Site Drainage area information revised. Entire Site Column drainage
area information revised. Design volume revised for each SCM.
C. Wet Pond Page:
i. Lines 2, 26, 27, & 35 — Revise as needed in accordance with other comments.
ii. Line 25 — The temporary pool surface elevation is typically equal to the invert elevation of the lowest
bypass weir in the pond outlet structure
iii. Line 32 — The forebay volume values for Wet Ponds 2, 3, 5, & 6 do not appear to match the
information provided in the stage -storage tables. For example, the form shows the permanent volume of the
forebay pool for Wet Pond 2 as 4,641 cf while the provided stage -storage tables indicate 3,999 cf. This
issue is also present with the other noted SCMs. Please revise as needed.
iv. Line 42 — There do not appear to be berms or baffles added to these ponds to increase the flow path
(berms added to separate the forebay from the main pool do not count for this, this item is asking if there
are any berms/baffles added to the pond design to increase the flow path from the inlet to the outlet).
LID Response: Minimum required treatment volume revised for all SCMs. Temporary pool elevation revised
for all SCMs. Forebay volume revised for all SCMs. Line 42 answered changed to 'NO' for all SCMs. No
berms or baffles are proposed apart from the forebay berm.
17. Provide PDFs of all revisions, 2 hardcopies of revised plan sheets, 1 hardcopy of other documents,
and a response to comments letter briefly describing how the comments have been addressed.
LID Response: PDFs of all revisions to be uploaded via the supplemental upload form. Hardcopies to be
provided of all revisions.
PDFs must be uploaded using the form at:
https://edocs.deq.nc.gov/Forms/SW-Supplemental-Upload
Hard copies must be mailed or delivered to the following address:
For FedEx/UPS: Jim Farkas
512 N. Salisbury Street, Office 640E Raleigh, NC 27604
For USPS: Jim Farkas
1612 Mail Service Center Raleigh, NC 27699-1612
iii. Hand Delivery: Please reach out to me prior to hand delivering a submission to make sure that I (or
someone else in my group) will be able to receive the submission. Do not leave the package in the foyer
with the security guard.
Sincerely,
Frank McMahan, PE for LandDesign, Inc.
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